1. Field of the Invention
This invention relates to inlet geometry for introducing working fluid into a turbine whose rotor is comprised of spaced apart discs. The inlet geometry directs the fluid in a manner which allows the turbine to accelerate to operating speed from standstill or from very low initial velocities.
2. Description of the Related Art
Turbines comprised of spaced-apart rotor discs were first described by Nikola Tesla in U.S. Pat. No. 1,061,142 and 1,061,206. For this reason, these turbines are sometimes referred to as Tesla Turbines, but are alternatively known as Prandtl layer turbines, boundary layer turbines, cohesion-type turbines, and bladeless turbines.
The turbine rotor consists of a stack of discs spaced apart and fixed to a rotatable shaft. The rotor assembly is contained in a housing closely fitted to the perimeter of the discs. The discs have vents near the center, and the housing includes at least one outlet near the center. In operation, an energetic working fluid at pressure and temperature is introduced at the periphery of the disc stack and contained in a housing which closely follows the perimeter of the discs. The working fluid passes between the discs and exits the stack assembly through vents near the center, leaving the housing through its outlets.
As the fluid enters the spaces between the discs, it exchanges a portion of its momentum to them through viscous adhesion of the fluid to the surfaces of the disc. Since the discs are constrained to rotate about the axis of the shaft, the motion attained by extraction of momentum of the fluid is axial rotation. The axial rotation of the discs in turn drags the fluid in a tangential direction, effecting a spiral flow of the working fluid.
The tangential component of the flow creates centripetal force within the working fluid, which must be overcome by additional fluid entering the housing. Therefore, in the steady state, great back pressure is developed at the inlet of the machine, along with a significant drop in pressure between the inlet and the outlet of the machine. This drop in pressure, with its concomitant drop in temperature and expansion of the working fluid, efficiently extracts much of the available thermodynamic energy of the working fluid.
The prior art devices introduce the working fluid at the rim of the discs in a tangential direction. Two examples of this design are given in FIGS. 1A and 2A and their enlargements in FIGS. 1B and 2B. It fact, the ability of working fluid to accelerate stationary or slow moving discs depends on the injection angle, which is the angle formed between the direction of the entering working fluid and a tangent to the disc periphery at a point intersected by the direction of the entering fluid.
Prior art inlets also include deleterious features such as sharp transitions along the internal passage, and features which abruptly alter the direction of fluid flow immediately prior to its entry into the disc rotor housing. Such sharp transitions create undesired turbulence in the working fluid and frictional losses which reduce the overall efficiency of the turbine. Enlargement FIG. 1B especially illustrates an inlet design inhering both abrupt sectional changes and an abrupt directional change of the internal passage through which working fluid is admitted.
A further limitation of the prior art is that the devices are not reliably self-starting; typically the shaft and the discs coupled to it must be in motion before the working fluid is able to accelerate the turbine to its steady-state operation. Typically the initial rotational speed of the turbine must be significant, for example on the order of at least one-tenth of the steady-state operating speed. The prior art devices therefore rely on external energy sources and motive means to provide initial rotation of the discs. These external means detrimentally add expense, size, weight, and mechanical complexity to a disc turbine system.
The benefit secured by a self-starting design is the elimination of the auxiliary components required in a system dependent on initial rotational speed for acceleration to operating speed. The benefit gained by a nearly self-starting design is the significant reduction of power output demanded or service hours required of these auxiliary components, and a concomitant reduction in expense, size, and weight of this auxiliary system.
It is therefore advantageous to provide a means of directing the influx of working fluid so that the passage of the fluid between stationary or nearly stationary discs of the rotor assembly is sufficient to accelerate the rotor assembly to operating speed.
According to the present invention, an inlet for a disc turbine is optimally placed on a housing for a disc turbine, and the direction of entering fluid as imparted by the geometry of the inlet is optimally aimed at a predetermined injection angle, so as to afford self-starting of a stationary set of rotor discs and swift acceleration of a disc rotor assembly already in motion.
Accordingly, Several Objects of the Invention Exist
An object of the invention is to provide the design parameters by which an inlet component of a spaced-disc turbine may be formed, so that working fluid directed through this inlet will accelerate a stationary or nearly stationary rotor assembly up to operating speed.
Another object of the invention is to precisely locate the inlet and its nozzle onto the rotor housing so that the ingress direction of the working fluid conforms to a desired injection angle as defined and explained further.
In this regard, a further object of the invention is to effect a seal of the inlet onto the housing so as to eliminate the escape of working fluids, which would otherwise present an operating hazard or a loss of inlet pressure.
A yet further object of this invention is to collect and concentrate the working fluid in a manner which reduces turbulent or frictional losses, by eliminating abrupt or sharp sectional changes of the inner surfaces of the turbine inlet, and to provide smooth sectional changes instead.
Yet another object of this invention is to reduce turbulent or frictional losses by eliminating abrupt changes in direction of the working fluid, and to provide smooth and especially arcuate directional changes instead.
An additional object of this invention is to impart stability and robustness to the reducing section of the inlet body so as to robustly resist torques and bending moments applied during connection of the assembled inlet to a fluid supply pipe.
The inlet may be an integral portion of a housing, such as a cast housing which includes an inlet section, or the inlet may be a discrete component which is affixed to the housing by attachment means. In this latter case, registration of the inlet to the housing is required during assembly, so that said assembly process located, aligns, and positions the nozzle orifice at its desired injection angle relative to the rotary motion of the discs.
For an inlet which is a discrete component from the housing, leakage of working fluid from between the inlet and housing must be eliminated, and therefore it is advantageous for the inlet to provide one or more contoured or planar surfaces which closely match accepting surfaces on the housing, so as to effect a fluid seal at their faces.
This seal may be effected by means of caulking or gasket material deposed between the sealing faces, or simply by sufficient mechanical compression of the inlet faces against the housing faces. More specifically, the sealing faces of the inlet may be in the form of a flange which mates against a complimentary surface on the housing.